The present invention relates to a medical needle or a cutting tool that does not produce rust and that provides high hardness as well as difficult bending property, and that further has non-reflectivity.
The medical needle includes, a suture needle used for suturing the affected area that has been incised or a needle used for blood drawing or fluid infusion, a reamer or a file used for performing root canal forming in dental treatment and the like. The medical cutting tool includes a surgical knife or a knife used when incising the affected area. Thus, the medical needle and the cutting tool have suitable shape in accordance with the intended use.
All of the above mentioned medical needle and the cutting tool have a function of piercing directly through the body tissue and passing the suture thread, or a function of scraping the structure of the teeth or a function of incising the body tissue. In such medical needle or the cutting tool, a force acts in a bending direction when performing the intended task, or a resistance when piercing through the body tissue, a resistance when scraping, or a resistance when cutting may act.
The treatment instrument for the root canal forming in the dental treatment is often required to scrape the hard layer of the surface of the teeth, and thus needs to have high hardness. On the other hand, when broken by an obstacle while working in the root canal forming, the task of removing the broken distal end portion is not easy. That is, the dental treatment instrument must have both a hard cutting blade and a high-level of difficult bending property. Since such medical needle or cutting tool directly contacts the body tissue, it is configured using a material that has no adverse effect on the body tissue.
Thus, in actual condition, the needle or tool that is not easily bent during use and has small resistance is continuously being developed in each manufacturing corporations.
A material having high hardness must be used to reduce the resistance when piercing, scraping or incising the body tissue, and to produce high resistance with respect to the bending force, and hardening processed steel or martensitic stainless steel is commonly used for such material. However, in the medical needle or cutting tool that uses such material, occurrence of rust in the circulation step is difficult to avoid.
Thus, the applicant of the present invention has developed a medical needle that has high hardness obtained through work hardening by performing cold pulling work on the austenite stainless steel, and that achieves difficult bending property by having fiber shape structure which is extended from the granulated austenite structure (refer to e.g. Japanese Patent Application Publication (JP-B) No. 1-11084). The medical needle obtained through such technique has advantages in that rust is not produced, sharpness of the cutting blade is ensured by having high hardness, and further, difficult bending property is obtained since the structure is extended into a fiber shape.
Since hardness due to thermal treatment cannot be expected in the austenite stainless steel, work hardness involved in cool working must be expected, as in the technique of JP-B No. 1-11084. Therefore, since the process for obtaining hardness is only through cold working, the types of products that can be applied to are extremely limited, and in order to overcome such problem, a technique of forming a hardened layer by performing carburization process on the austenite stainless steel has been developed (refer to e.g., Japanese Patent Application Laid-Open (JP-A) No. 9-268354).